1. Field of the Invention
The present invention relates to the art of copying and printing machines, and more particularly, to an image reader in this art for photoelectrically reading out an image of an original to generate a corresponding electric signal.
2. Description of the Prior Art
There has been long known and widely used such an image reader that has a casing, a stage glass mounted to the casing for supporting an original bearing an image to be read out thereon with the image facing downward, a press plate adapted to be optionally laid over the stage glass for pressing the original placed on the stage glass thereto, a photoelectric image reading head having a light source means for projecting light beams to the original placed on the stage glass from a lower side thereof therethrough and a photoelectric converting means for receiving and converting light beams reflected from the original into an electric signal corresponding to the image.
With regard to such a reflection type image reader, it has been proposed by Japanese Patent Laid-open Publication Sho 59-165044 to provide illumination means below the four corners of the stage glass to facilitate an action of confirming the position of an original placed on the stage glass prior to the reading out thereof in apprehension of the original being displaced as a result of pressing by the press plate, as it often occurs when an open page of a book is the original to be read out. Further, it has been proposed by Japanese Patent Laid-open Publication Sho 61-295549 to operate a scanning type image reading head for about two times of scanning reciprocation with an actuation of only the illumination means thereof in response to a pressing of a switch for confirming the position of the original so that an action of confirming the position of the original under an illumination is available in the meantime. Still further, it has been proposed by Japanese Patent Laid-open Publication Hei 3-13932 to draw some reference marks for positioning originals such as frames by lines showing the contours of several regular sheet sizes on the stage glass with a fluorescent material observable by human eyes but not responded by the photoelectric image reading head, in addition to a provision of the illumination means below the stage glass for confirming the positions of originals.
When the reference marks for positioning originals such as the frames by lines are provided in the stage glass as proposed in the above-mentioned Publication Hei 3-13932, the reference marks must be such that are observable by human eyes but not responded by the photoelectric image reading head as described above. Still further, when the reference marks are such frames of lines showing the regular sizes of sheets, although a coincidence of a peripheral edge of an original with a frame of line is directly observable as looked down from above when the original is a sheet of a regular size, if an image, not a peripheral edge, of an original is to be positioned relative to the stage glass at a particular positional or directional relationship, the reference marks provided in the stage glass are not directly observable from above as they are covered by the original. Therefore, even when an illumination means is provided under the stage glass, the reference marks in such a thickness as to be not responded by the photoelectric image reading head will not be clearly observable from above through the original.